Hemodialysis apparatus with degassing means for the dialysis solution

ABSTRACT

The ultra-filtration in a hemodialysis operation is controlled by a control apparatus which is connected to a balancing device (1) and to a dosing device (9) to form a closed loop control circuit for the metered supply of dialysis concentrate into the balancing device and for the metered supply of fresh dialysis solution into the dialyzer. The closed loop control circuit controls the alternating supply of fresh dialysis solution into one chamber of a balancing device and the withdrawal of used-up dialysis solution from the other chamber of the balancing device. The closed loop control circuit also controls a pump for the metered withdrawal of used-up dialysis solution out of the dialysis circulatory system. The dosing device operates as a proportionality device to produce fresh dialysis solution from water and dialysis concentrate whereby the concentrate is dosed and the dialysis solution is also dosed or metered.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of my copending applicationSer. No. 406,711, filed Aug. 9, 1982 (now abandoned) which was acontinuation application of U.S. Ser. No. 198,912, filed Oct. 20, 1980,now abandoned. U.S. Ser. No. 198,912 was a continuation-in-partapplication of U.S. Ser. No. 69,387, filed on Aug. 24, 1979, now U.S.Pat. No. 4,267,040, issued on May 12, 1981.

BACKGROUND OF THE INVENTION INCLUDING PRIOR ART STATEMENT

The invention relates to a control of the ultra-filtration in connectionwith hemodialysis. A control apparatus controls the alternate supply orwithdrawal of fresh and used dialysis solution into one or the other orout of one or the other chamber of at least one balancing apparatus andfor controlling the drive of an ultra-filtration pump for an additionalwithdrawal of used dialysis solution out of the dialyzer circulatorysystem.

A known method for the discontinuous measuring of the liquid withdrawalper unit of time resides in that the dialyzer solution flow to thedialyzer is temporarily interrupted by means of switch-over valves andin that the outflow conduit of the dialyzer is connected with a throughflow meter for reading the liquid withdrawal per unit of time. By meansof additional steps the pressure difference between the blood side andthe dialyzing solution side is kept constant on the previous operationalvalue. Thus, the passage of liquid through the membrane during themeasuring is about the same as during the normal operation. It isdisadvantageous, that each time it is necessary to interrupt theoperation so that a continuous measuring is not possible according tosaid method. Further, with said method only one measuring possibility isprovided. In order to achieve a determined value of the liquid quantityto be withdrawn it is necessary to evaluate the measured results and tomake a corresponding manual correction of the operating values in theapparatus at relatively short time intervals.

It is known from U.S. Pat. No. 4,113,614 to automate the control of thepressure across the membrane in a hemodialysis apparatus and also toautomate the control of the ultra-filtration rate by metering andmonitoring the ultra-filtration rate and the total quantity ofultra-filtrate removed. One embodiment of this U.S. Pat. No. 4,113,614which was issued on Sept. 12, 1978, requires a dialysis solutionreservoir having a constant volume. In another embodiment of this priorart two pumps are used having exactly corresponding pumping rates forthe supply and discharge of dialysis solution, whereby a dynamicallyclosed system is provided. However, it is in practice very difficult toconstruct pumps in an economically feasible way, which have exactlycorresponding pumping rates.

U.S. Pat. No. 4,113,614 also discloses a special pump for the withdrawalof liquid from the dynamically closed system in such a quantity that thequantity of withdrawn liquid corresponds to the ultra-filtrationquantity. A piston pump is disclosed for this purpose which is alsoutilized simultaneously for measuring the pumped quantity and, based onthe assumed proportionality of the driving force for the pump and theworking pressure of the pump, for measuring the pressure. This type ofapparatus leaves room for improvement, especially with regard to theproblem of proportioning the concentrate and water. More specifically,the preparation of the dialysis solution from concentrate and water inexactly predetermined ratios in combination with the supply and removalof liquid quantities corresponding to each other may be improved upon,particularly if these mentioned partial functions are to be directlycombined or linked with each other as is the purpose of the presentinvention.

An article by Harold P. McDonald, Jr., entitled "Automatic PeritonealDialysis Machine for Hospital or Home Peritoneal Dialysis; PreliminaryReport" appeared in volume 15 of the "Transactions of the AmericanSociety of Artificial Internal Organs", (1969) starting at page 108 andending on page 111. A peritoneal dialysis apparatus is not necessarilysuitable for hemodialysis purposes. For example, in a peritonealdialysis apparatus a single state system is used in a discontinuousoperation with piston pumps. The ultra-filtration is not controlled andthe ultra-filtrate quantity may be measured only at certain times,namely, at the end of the flow out time by measuring the liquid level inthe flow out container. Thus, the teachings applicable to a peritonealdialysis apparatus are not suitable for a hemodialysis apparatusespecially where the latter is supposed to operate continuously in apush-pull fashion to assure a continuous, uniform flow through thedialyzer. Moreover, the control of the ultra-filtration with apredetermined ultra-filtration rate in terms of ultra-filtrationquantity per unit of time, as well as a continuous indication of theaccumulated ultra-filtration quantity, is not taught by McDonald, Jr.

U.S. Pat. No. 4,037,616 (Pinkerton) discloses certain features which arealso employed according to the present invention, for example, the useof balancing chamber components operated in a push-pull type of system.However, Pinkerton actually uses the diaphragms and piston means or atleast piston rods which extend through the chamber walls and thus causeleakage problems at the points where the piston rods extend through thechamber walls, see for example FIGS. 1, 3, and 4 of Pinkerton. The typeof liquid used in dialysis comprises a high proportion of salt andglucose in solution. Therefore, there is a strong tendency for thesecomponents in solution to crystallize, and experience has shown thatsuch crystallization takes place on the piston rods, whereby thesealings at the passage points through the chamber walls are damaged bythe crystalline material. This crystallization is a continuous processand once a leakage has formed it grows rapidly.

Moreover, in this environment it is, for the patient's health, veryimportant to keep the entire system free of infection causing agents.Piston rods as in Pinkerton cannot be kept entirely free of suchinfecting agents because the piston rods extend into and out of thebalancing chamber components.

Kunitomo et al in the article "Controlled Ultrafiltration WithHemodialysis", Trans. Am. Soc. Int. Organs, Volume 23, pages 234 to 242(1977) also do not disclose the combination of teachings for theproportional mixing of the two components which are used to make freshdialysis solution and there is also no teaching in Kunitomo et al tocombine the mixing with a balancing operation. While it is true thatKunitomo et al discloses a degasser in FIG. 2 on page 235, applicantdoes not claim a degasser per se.

A second Pinkerton U.S. Pat. No. 4,054,522 also suffers the same defectsas the first mentioned Pinkerton reference (U.S. Pat. No. 4,037,616) andthe comments above apply also to the second Pinkerton referenceincluding FIG. 3 thereof.

U.S. Pat. No. 3,976,574 (White) shows two degassers (22) and (26).However, these two degassers or aerators are connected in series throughthe mixer (24) and hence both aerators are effective on the liquid whichis supplied to the dialyzer (10). According to the present invention theaerators or degassing means are arranged quite differently. The presentinvention is more importantly concerned with balancing andultra-filtration control.

U.S. Pat. No. 3,795,318 (Crane et al) was primarily cited for itspressure sensing features. However, the present invention is notexhausted by such a feature and aims at a switch-over of the balancingchamber components from push to pull and vice versa in response to apressure sensing. Thus, the respective valve means at the inlets of thebalancing chamber components are switched from one into the otherposition if the pressure in the return conduit from the dialyzer at theoutlet of the pump (67) in FIG. 8 exceeds a predetermined pressurevalue.

The control of a switch in response to a pressure sensitive element isshown in U.S. Pat. No. 3,709,222 (DeVries) "Method And Apparatus ForAutomatic Peritoneal Dialysis", however, the just mentioned referencedoes not disclose the combination of the features set forth hereafter.Therefore, even if the disclosure of DeVries is combined with thedisclosure of the Pinkerton reference U.S. Pat. No. 4,037,616 theteachings of the present invention cannot be found.

U.S. Pat. No. 4,060,485 (Eaton) shows the use of a "computer" in adialysis apparatus. However, there are no details shown in the Eatonreference to the effect that two temperature controlled heating unitsare employed for improving, or rather increasing the balancing precisionas disclosed with reference to present FIG. 4. The present temperaturecontrolled system of the present application assures that thetemperature difference between the inflowing and outflowing dialysate issubstantially zero and that the temperature of the dialysate in thedialyzer corresponds to the patient's temperature. No such teaching isdisclosed by Eaton.

U.S. Pat. No. 4,113,614 shows an ultra-filtration rate read-out unit.However, the present invention is not exhausted by such a feature.

U.S. Pat. No. 3,352,779 discloses the filling of the hemodialyzer priorto its operation. While it is necessary to fill the dialyzer prior toits operation, Austin et al do not give any hint of the specific waythis is accomplished according to the present invention.

U.S. Pat. No. 4,054,522 shows, in FIG. 3, the sequential arrangement ofa dosing and mixing system (A) with a degassing system (B) and theultra-filtration system (C). These three systems (A, B, and C) of U.S.Pat. No. 4,054,522 operate substantially independently of one another.Therefore, the cooperation as set forth in the present case of theproportioning and mixing system with the remaining features is notdisclosed in U.S. Pat. No. 4,054,522. According to the present inventionthe concentrate only is directly dosed and the water is dosedindirectly. The balancing system acts as a meter for the quantity ofused-up dialysis solution whereby a connection between the balancingfunction and the proportioning is accomplished. This is not shown inU.S. Pat. No. 4,054,522.

French Patent No. 2,344,297 shows the use of an alarm in a hemodialysissystem when the blood transfer level is not acceptable. Although thisFrench patent shows two balancing chambers, it does not disclose thefunctional or operational combination of the balancing operation whichthe dosing and mixing operation. Further, the detector in Frenchreference No. 2,344,297 is a hemoglobin detector in the form of a"colorimeter 23" which cannot be compared with the present blood leakagedetector (65) in FIG. 8.

German Patent Publication No. 2,544,258 which is based on anotherinvention of the present inventor, was also cited for the alarm feature.In this earlier system, of the present inventor, the operation is not apush-pull operation so that a filling step is required between twoworking steps or strokes. During the filling step dialysate does notflow through the dialyzer. Moreover, the balancing is not directlyrelated to the dialysis solution as it is prepared and flowing into thedialyzer. In this reference the components of water and concentrate onthe one hand, and the used-up dialysis solution on the other hand, arebalanced.

In French Patent No. 2,345,165 the production of the dialysis solutionwith the step of proportional mixing of the concentrate and water isindependent of the balancing and independent of the ultra-filtrationcontrol. Therefore, a more detailed discussion of this reference doesnot appear to be necessary.

Netherlands' Patent Publication No. 7,701,451 appears to be quitesimilar to the Pinkerton reference U.S. Pat. No. 4,037,616 which hasbeen discussed in detail above. Therefore, a further discussion of theDutch reference would appear to be unnecessary.

Ivanovich et al in the article "A Compact Hydraulic Proportioning SystemFor Hemodialysis", Trans. Am. Soc. Int. Organs, Vol. 12, pages 357 to361 (1966) provides an alternative to the French Patent No. 2,344,297with regard to the alarm feature and is pertinent only to that feature.Therefore, a further discussion of this Ivanovich et al reference doesnot appear to be necessary. Furthermore, in Ivanovich et al the waterand concentrate are dosed by piston pumps. Contrary thereof according tothe present invention, the through flow of the ready dialysis solutionalready mixed is measured and this measuring controls the portion-wisesupply of the concentrate to a mixing point arranged upstream of thebalancing chamber.

Applicant notes the following additional reference, all of which may beclearly distinguished from the present invention:

U.S. Pat. No. 3,920,556 (Bowman); No. 3,939,069 (Granger et al); No.3,979,284 (Granger et al); No. 3,990,973 (Boag et al); No. 4,008,003(Pinkerton); No. 4,021,341 (Cosentino et al); No. 4,083,777(Hutchisson); No. 4,093,545 (Cullis); No. 4,096,059 (Pinkerton); No.4,119,113 (Meginniss, III); No. 3,946,731 (Lichtenstein); No. 3,579,441(Brown); and No. 3,709,222 (DeVries).

OBJECTS OF THE INVENTION

In view of the above it is the aim of the invention to achieve thefollowing objects singly or in combination:

to construct a hemodialysis apparatus so that the dosing of freshdialyzing liquid to be supplied takes place automatically on the basisof the operation of a balancing apparatus and to make possible acontinuous display or control of the rate of ultra-filtration;

to provide a control circuit for a hemodialysis apparatus which respondseither to the throughput of certain volumes or masses of the dialysissolution or it may respond to a pressure difference caused by volume ormass differences;

to effectively remove gas bubbles especially air bubbles from the entirecirculatory system thereby to increase the efficiency of the dialyzingoperation;

to control the push-pull type of operation of the dialysis solutionbalancing system by means of valves which may be switched by electric orelectronic control signals;

to provide a continuous flow of dialysis solution by means of passivelyoperated, fixed volume membrane pumps whereby piston operations and therespective leakage problems are avoided;

to supply the components for making the dialysis solution under reducedpressure or atmospheric pressure at the most and to supply the freshdialysis solution at a pressure larger than atmospheric pressure; and

to keep the circuits for fresh dialysis solution hermetically sealedfrom the circuits for the used dialysis solution to avoid any dangerousinfection.

SUMMARY OF THE INVENTION

According to the invention there is provided an apparatus for theultra-filtration control in a hemodialysis operation in a dialysiscirculatory system including a dialyzer, wherein control means controlthe alternate supply or discharge of fresh and used-up dialysis solutioninto one or into another or out of one or out of the other chamber of atleast one balancing device, said control means also controlling thedrive of an ultra-filtration pump for the additional withdrawal ofused-up dialysis solution out of the dialysis circulatory system,wherein the control means are connected with a balancing device and witha dosing apparatus for the supply of the dialysis concentrate, whereby acontrol unit including a control circuit is formed.

BRIEF FIGURE DESCRIPTION

In order that the invention may be clearly understood, it will now bedescribed, by way of example, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a simplified basic diagram of the dialysis solutioncirculatory system with a balancing device;

FIG. 2 shows a simplified basic diagram of the dialysis solutioncirculatory system in which the functions of the balancing and of theproportional dosing are combined and in which both functions aremonitored in common;

FIG. 3 is a more detailed illustration of the schematic diagramaccording to FIG. 2;

FIG. 3A is a circuit arrangement for controlling the balancing deviceand the dosing apparatus;

FIG. 4 is a further embodiment of the arrangement according to FIG. 1for compensating temperature caused errors in the mass balance;

FIG. 5 is a block circuit diagram for calculating the compensation ofthe influence of temperature differences;

FIG. 6 shows a schematic sectional view of an example of a balancingchamber;

FIG. 7 is another extended embodiment of the arrangement according toFIG. 1 for venting the dialyzer circulatory system;

FIG. 8 is a detailed illustration of the liquid circulatory system of ahemodialyzing apparatus;

FIG. 8A shows a detail of the circuit of a pump motor of FIG. 8; and

FIG. 9 is a sectional view through an example embodiment of a dosingapparatus.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

The relevant portion of the liquid circulatory system in FIG. 1 is shownsubstantially simplified and schematically for explaining the principleof operation of a balancing device. The balancing device 1 is animportant component of this arrangement. The balancing device comprisestwo chambers 1a and 1b connected to each other. The first chambercooperates with the supply conduit 2 for the fresh dialysis solution.The second chamber 1b cooperates with the discharge conduit 3 for theused-up dialysis solution. The balancing device makes sure that thequantity of the fresh dialysis solution flowing through the conduit 2ato the dialyzer 4 corresponds exactly to the used-up dialysis solutionflowing out of the dialyzer through the conduit 3a. Due to thischaracteristic of the balancing device it is not possible that underthese conditions a volume shift between the blood side of thesemi-permeable membrane 5 and the dialysis solution side of thismembrane takes place in the dialyzer 4. Such shift cannot take place inone or the other direction. The other side of the membrane 5 isconnected to the patient through the conduits 6.

Thus, the so-called ultra-filtration rate is zero. The portion of theliquid circulatory system enclosed between the balancing device 1 andthe dialyzer 4 acts as a closed system having a constant volume. Awithdrawal device 7 is connected to a discharge conduit 8 in order toremove liquid from this system.

The liquid quantity removed from the system by means of the withdrawaldevice must be replaced by an equal liquid quantity due to the mentionedcharacteristics of the balancing device, said liquid quantity passingfrom the blood side to the dialyzing solution side of the dialyzermembrane. Thus, the liquid quantity removed by means of the withdrawaldevice corresponds to the liquid quantity passing through the membraneof the dialyzer 4 and thus it corresponds to the ultra-filtrate. Thewithdrawal device may now be constructed so that a control of theultra-filtration may be achieved. According to the invention, theultra-filtrate withdrawal device is, for example, a constant volumemembrane pump. The rate of pumping and therefore the rate ofultra-filtration may be automatically controlled in response to measuredparameters of the dialysis circulatory system for optimum levels bycomputer means or analog feedback signal means.

The precision of the balancing device must meet very high requirements.Typically, about 200 liters of the dialysis solution are passed throughthe dialyzer during a hemodialysis treatment. The ultra-filtrationquantity corresponds typically to about 2 to 3 liters. This quantityshould be determinable except for a deviation in the order of 0.1 to 0.2liters. Thus, the balancing error caused in the balancing device shouldnot, if at all possible, exceed the order of 1 per mill (one perthousand). The patient may be exposed to a substantial danger if alarger balancing error occurs and remains unnoticed due to a technicalerror, for example, due to the failure of a structural component. Thus,it is necesary that the balancing device satisfies the requirement thata functional error is automatically detected and that an alarm is givenif an error occurs.

In the present type system the necessary safety against functionalfailure of the balancing system is achieved in that the balancing unitis not only constructed for the balancing of the inflow and outflow ofthe dialysis solution, but also it is simultaneously connected to thedosing device to form a control circuit or unit.

The principle of a correspondingly extended arrangement is illustratedin FIG. 2. The same components are provided with the same referencesymbols as in FIG. 1.

Additional elements for realizing a proportional dosing function and formonitoring the proprotional dosing function comprise a dosing apparatus9 and an analyzing device 10. The dosing apparatus 9 is supplied througha conduit 11 and in turn supplies into the conduit 2 through aconnection 12. The analyzing device is connected directly into theconduit 2 between the balancing chamber 1 and the dialyzer 4.

It is a requirement for the intended function of the illustratedarrangement that the balancing device 1 has a periodic type of operationin which the balancing device passes on a precisely defined dialysissolution volume for each operating period. For this defined dialysissolution volume a volume of concentrate is necessary which has a fixedratio to the defined dialysis solution volume. The volume of concentrateis supplied also through the dosing device 9 in a periodic mannerwhereby the balancing device 1 and the dosing apparatus preferablyoperate in synchronism with each other.

The water supplied through the conduit 2 and the concentrate supplied bythe dosing apparatus 9 form, after their mixing, a dialyzing solution ofthe desired composition if the quantitative ratio has been correctlyadjusted. The composition is monitored by the analyzing device connectedinto the conduit to the dialyzer. The components serving in thebalancing device for the metering of the volumes simultaneouslydetermine the liquid volume conveyed during each working period.Therefore, it is possible, by using the analyzing device 10 to monitorthe operation of the proportional dosing as well as indirectly theoperation of the balancing.

Details shall be explained with reference to the example illustrated inFIG. 3. The balancing device comprises the balancing chambers 22 and 23and the respective valves 14 to 21. The balancing device forms togetherwith the dosing apparatus 9 a proportional dosing system which mixes theconcentrate and water in a predetermined quantity ratio. The analyzingdevice 10 measures one or several parameters which are characteristicfor the composition of the mixture, whereby a control of the mentionedfunctions is possible. For example, an output of the analyzing device 10is connected for controlling a valve 62 as shown by the dashed line 83'in FIG. 8.

Both chambers 22 and 23 are an essential component of the balancingdevice. Basically, these chambers comprise fixed volume hollow bodieseach including two spaces which are separated from each other by amovable, tightly closing flexible element 24 or 25. Thus, when one ofthe spaces is increased in size, the size of the other space isnecessarily reduced to the same extent. In the schematic illustration ofFIG. 3 the chambers 22 and 23 are, for example, spheres, and the movableelements 24 and 25 are membranes. Having regard to the dosing function,it is further important for the actual construction of the chambers andthe elements movable therein that the displacement of the movableelements from one extreme position into the other results in areproduceable volume displacement. This feature is achieved, forexample, in the embodiment of FIG. 3 in that the membranes 24 and 25 intheir extreme positions rest completely against the right or left wallof the respective chamber so that upon movement from one extremeposition into the other a volume shift takes place corresponding in itsvalue to the entire chamber volume.

The valves 14 to 21 arranged for cooperation with the balancingchambers, form two groups which are operated alternately. If the valvesof the group A (valves 15, 17, 18, and 20) are opened, the valves of thegroup B (valves 14, 16, 19, and 21) are closed and vice versa. Thus, thetwo chambers operate in push-pull fashion whereby their respectivefunctions are periodically exchanged. During the time when one of thetwo chambers is respectively connected into the circulatory system 2a,3a of the dialyzer, the other chamber is charged with new dialysissolution while simultaneously the used-up dialysis solution is displacedinto the discharge conduit 3.

If the valves of the group A (illustrated in dark) are opened, and ifthe valves of the group B (lightly illustrated) are closed, the chamber22 is charged with fresh dialysis solution while the chamber 23 servesfor supplying the dialyzer. The charging of the chamber 22 is achieveddue to the fact that fresh solution flows under pressure through theopened valve 18 into the space 22a. Thus, the membrane 24 yields and theused dialysis solution present in the space 22b on the other side of themembrane is displaced through the opened valve 15 into the dischargeconduit 3. When the membrane rests entirely against the right-handchamber wall, this charging operation is completed.

During this time the dialyzer is supplied from the chamber 23 in thatthe fresh dialysis solution present in the space 23a is conductedthrough the opened valve 17 and through the conduit 2a to the dialyzer.This solution is returned as used-up dialysis solution from the dialyzerthrough the conduit 3a and the opened valve 20 into the space 23b of thesame chamber. Due to the fixed volume of the balancing chamber thereturned quantity of liquid must necessarily correspond exactly to thequantity of liquid supplied into the dialyzer. The dialyzing solutionflows thus in a quasi-closed circulatory system because the beginningand the end are connected to each other in the balancing chamber bymeans of the displaceable element. However, a mixing of fresh andused-up dialysis solution does not take place. As soon as the membranein the chamber 23 rests completely against the right-hand chamber wallthe operation is completed. In order to maintain the through flowthrough the dialyzer, merely, the valves are switched over so that thetwo chambers of the balancing device exchange their function.

If now the valves of group A are closed and the valves of group B areopened, fresh dialysis solution may continue to flow to the dialyzerthrough the opened valve 14 from the space 22a of the chamber 22. Duringthis time the same quantity of used-up dialysis solution is returned outof the dialyzer through the opened valve 19 into the space 22b on theother side of the membrane. At the beginning of this operation the space22a is in its maximally filled condition whereas the space 22b is in itsminimally filed condition because during the preceding work period thespace 22a was filled completely with fresh dialysis solution asdescribed. During the time when the dialyzer is supplied from thechamber 22, the chamber 23, is being charged with fresh dialysissolution. At the beginning of this time the space 23b is filledcompletely with used-up dialysis solution as the result of the precedingwork period. The fresh dialysis solution flows through the opened valve21 into the space 23a and the used-up dialysis solution present in thespace 23b is displaced through the opened valve 16 into the dischargeconduit 3.

The switch over of the valve groups must respectively occur when thesupply in the balancing chamber which presently feeds into the dialyzer,is exhausted. The charging of the other balancing chamber should becompleted at this time. Such completion may be achieved by arespectively high charging speed without difficulties. The signal forthe switch over of the valves may be obtained in different ways. Theflow of dialysis solution in the dialyzer circuit stops as soon as themembrane in the balancing chamber which feeds the dialyzer reaches itsextreme position. Therefore, it would be possible to use a through flowmeter with a device for providing a signal output when the flow fallsbelow a minimum flow. Another approach uses pressure responsive endposition sensing using the pressure change resulting as the membranereaches the end position for triggering the switch over function.Further, known methods may be employed which provide a direct indicationwhen the membrane reaches the end position, for example, micro-sensorsmay be used.

The balancing device takes up a certain quantity of dialysis solutionduring each working stroke or period when it is working as described.This quantity of dialysis solution is defined by the volume shiftoccurring due to the two extreme positions of the movable element in thebalancing chamber. For each volume unit taken up by the balancingdevice, it is necessary to supply the respective quantity of concentrateto the supplied basic liquid (for example, distilled water) in order toproduce by mixing the concentrate and the liquid in the intended ratio,the dialysis solution having the desired composition and concentration.The addition of the concentrate is accomplished by the dosing apparatus9. The dosing apparatus may, for example, be constructed as a dosingpump which supplies by means of one or several pump strokes the quantityof concentrate necessary for one filling of the balancing chamber. Theoperation of the dosing apparatus is controlled in synchronism with theswitching over of the valves 14 to 21. Stated differently, during eachcharging operation of one of the balancing chambers 22 or 23 therequired quantity of concentrate is called up and mixed into the waterflowing in simultaneously. In FIG. 3 the mixing conduit is directlyconnected to the supply conduit 2 of the balancing device. However, thisis not at all necessary. It may be more advantageous to carry out themixing of the concentrate into the water in a component preceding thewater treatment system proper or the mixing may be done directly at thewater inlet of the apparatus, among others, for the purpose of achievingan intermixing of the concentrate and the water which is as homogeneousas possible.

The analysis device 10 monitors in a manner known as such thecomposition of the dialysis solution which flows to the dialyzer. It iscustomary to use for this purpose a meter measuring the electricalconductivity. However, other analysis devices may be employed, forexample, ion selective electrodes. However, it is essential that in anapparatus according to the invention now only the function of theproportional dosing of concentrate and water is monitored with the aidof the analysis device, but indirectly also the balancing function. Thatis to say, if a defect should occur in one of the structural componentsof the balancing device, for example if one of the valves 14 to 21fails, or if one of the membranes 24, 25 springs a leak, or if thebalancing chamber springs a leak outwardly, the dosing function isimpaired thereby which results in a corresponding deviation of thecomposition of the dialysis solution. In such instances an alarm signalis caused by the customary limit value monitoring of the analysisdevice. In addition, the apparatus may be automatically switched off inorder to prevent further effects of the fault.

The arrangement illustrated in FIG. 3 has a further importantcharacteristic in that it provides the possibility to temporarilysuspend the balancing function while simultaneously maintaining thefunctions of the proportional dosing of concentrate and water. Forexample, this is important when a new dialyzer is put into operation inorder to initially fill the dialyzer with dialysis solution. Due to thecharacteristic features of the balancing system such initial fillingwould normally not be possible because the balancing system discharges aquantity of liquid equal to the liquid supplied into the balancingsystem thereby keeping the liquid volume in the dialyzer circulatorysystem constant.

The operation in which the balancing function is suspended isaccomplished by a different control of the valves. Starting with acondition in which one of the balancing chambers (for example 22a) iscompletely filled with fresh dialysis solution and the other balancingchamber (for example, 23b) is completely filled with used dialysissolution, the valves 19 and 20 and a valve 26 in the discharge conduitare closed. The valves 15 and 16 are opened and the valves 16 and 17 aswell as 21 and 14 form two groups which are opened and closed inalternating sequence. The control of the mentioned valve groups may beaccomplished on the one hand in the above described manner in responseto the detection of the extreme positions of the membrane, more simply,by means of a time clock pulse which is selected to be sufficiently slowso that the membranes will be in their end positions with certainty atthe time of the switch over.

When the valves 21 and 14 are being opened under the mentionedconditions while the valves 18 and 17 are closed, fresh dialysissolution flows through the valve 21 into the space 23a of the balancingchamber 23 thereby displacing out of the space 23b on the other side ofthe membrane a respective quantity of the liquid through the openedvalves 15 and 16 into the space 22b of the balancing chamber 22. As aresult, an equal quantity of fresh dialysis solution is displaced out ofthe space 22a and supplied through the opened valve 14 to the dialyzer.This operation ends when the membranes reach their extreme positions.

Thereafter the valves 21 and 14 are closed and the valves 18 and 17 areopened. The fresh dialysis solution now flows through the valve 18 intothe space 22a of the balancing chamber 22 and displaces through themembrane the solution present in the space 22b through the opened valves15 and 16 in the space 23b of the balancing chamber 23 whereby the freshdialysis solution previously filled into the space 23a is transmitted inequal quantity through the valve 17 to the dialyzer. After the membraneshave reached their extreme positions, a new switch-over of the valvegroups 18 and 17, and 21, 14 takes place so that the two chambers 22, 23again exchange their functions.

By the described manner of operation the dialysis solution istransmitted to the dialyzer in determined portions as in the normal,balancing type of operation. These portions are defined by the volumeshift which occurs between the two extreme positions of the movableelement in the balancing chambers. The dosing apparatus supplies theconcentrate in synchronism. Thus, the function of the proportionaldosing of water and concentrate remains in existence while the balancingis suspended.

A circuit arrangment for controlling the valves 14 to 21 and 26 as wellas the dosing apparatus 9 in accordance with the described function isshown in FIG. 3A. In this connection it is to be noted that merely asimple example embodiment is involved which may be replaced by othercircuit arrangements in a different manner. If the operation of thevalves and of the dosing apparatus does not take place by means ofsolenoids as is assumed herein, but rather, for example, by hydraulic orpneumatic means, it is possible to use control devices which operate inan equivalent manner according to the general state of the art withoutany difficulties.

The switch over from the normal balancing type of operation to thenon-balancing type of operation takes place by means of a relay 70having seven switch-over contacts to the terminals of which thesolenoids of the valves 14 to 21 are connected. In the illustrated restposition of the contacts the solenoids 14a to 21a and 26a of the valves14 to 21 and 26 are coordinated in two groups which are alternatelysupplied with current through the respective power amplifier 71 or 72 bymeans of a flip-flop 73.

The control signals from the end position detector of the balancingdevice are supplied through the conductor 74. They reach the poweramplifier 77 for activating the solenoid 9a of the dosing apparatus 9through a selector switch 75a and a timer 76 which produces a pulse or apulse sequence of a determined duration. Thus, a dosing operation iscaused for each switch over.

In order to switch the system over into the non-balancing type ofoperation, the mechanically coupled selector switches 75a and 75b arebrought into the position illustrated by a dashed line. Thus, thesolenoid 70a of the relay 70 conducts current so that the selectorcontacts thereof also take up the positions illustrated by dashed lines.The solenoids of the valves 19, 20, and 26 thus become de-energized sothat these valves remain continuously closed. The solenoids of thevalves 15 and 16 receive continuously the energizing current in order tokeep these valves open.

The valve groups 18, 17 and 21, 14 are alternately switched over by theflip-flop 80 through the power amplifier 78, 79. The control of theflip-flop 80 is accomplished by an impulse generator 81 which has beenenergized by actuating the selector switch 75b into the active state.The control pulses are simultaneously supplied to the solenoids 9a ofthe dosing apparatus 9 through the selector switch 75a, the timer 76 andthe power amplifier 77 so that the dosing apparatus 9 continues tooperate synchroneously with the switch over steps of the balancingdevice.

A further embodiment of the invention provides the possibility toreference the balancing to the mass of the inflowing and outflowingliquid. This is accomplished in that the temperatures of the liquidflows in the balancing device are made to correspond to each otherwhereby the influence of the dependency of the density of the liquid iseliminated. An arrangement for accomplishing this purpose is illustratedschematically in FIG. 4. The dialysis solution circulatory systemcomprises two continuous flow heaters H₁ and H₂ as well as threetemperature measuring sensors which measure the temperatures T₁, T₂, andT₃. The temperature sensor T₂ and the continuous flow heater H₃ formtogether with the electronic regulator 27 of the conventionalconstruction, a temperature control system 28 within a control devicewhich serves to bring the temperature of the dialysis solution suppliedto the dialyzer to an adjustable, rated value which corresponds about tothe human body temperature (about 38° C.). One must assume that thetemperature of the used-up dialysis solution coming from the dialyzer islower than the temperature of the solution supplied to the dialyzerbecause of heat losses to the environment. Thus, the temperature sensorwhich measures the temperature T₃ senses a lower temperature at theconnection of the connection of the return flow conduit 3a connected tothe balancing device. In order to provide the same conditions for bothcomponents 1a and 1b of the balancing device, the temperature measuredby the temperature sensor T₃ is used as a rated value for a temperatureregulating system which comprises the temperature sensor T₁, thecontinuous flow heater H₁ and an electronic controller. This regulatingsystem causes the equalization of the temperatures T₁ and T₃.

The invention provides in another embodiment that the temperaturedependency of the density and the influence caused thereby on thebalancing is taken into account by calculation. In connection with anexact volumetric balancing the balancing error caused by a temperaturedeviation and which is dependent on the masses given by the formula:

    Δm=0.167Q.sub.D ·(T.sub.3 -T.sub.1)β

wherein Δm is given in grams per hour. Q_(D) is the dialysis solutionflow in grams per minute, T₃ -T₁ is a temperature difference in degreesKelvin between the inlets of the balancing device and β is the cubicexpansion coefficient of the dialysis solution, about 3.7×10⁻⁴ ° K.⁻¹. Asignal proportional to the resulting calculation may be used to controlthe withdrawing device 7 and the rate of ultra-filtration.

The technical performance of the calculation operation is possible indifferent ways. The block circuit diagram of FIG. 5 which represents apreferred embodiment, is based on the assumption that the entirequantity of the ultra-filtrate is displayed on a display device 30, forexample, a digital display device. The display device is controlled by acounter or computer circuit 31, the input pulses of which represent arespective, determined unit quantity of the ultra-filtrate (for example,one gram). The counter receives input pulses through an OR-gate 32 fromthe withdrawal device 7 in FIG. 1 as well as from the correction circuitfor compensating the temperature influence. If the withdrawal device isa volumetric pump which conveys a unit volume per work stroke, thecontrol pulses of the pump may be applied directly to the input 33 ofthe OR-gate. In other instances it may be necessary to use, for example,an intermediate circuit comprising a voltage frequency converter.

For correcting the influence of the temperature difference T₁ -T₃ firstthe difference between the two electric signals is formed whichrepresent the temperatures T₁ and T₃, said difference being formed bymeans of the subtraction circuit 34. The difference T₁ -T₃ is multipliedby the multiplier 35 by an electrical signal corresponding to thethrough flow Q_(D). If the machine operates always with the samedialysis solution flow and if no operation adjustment for this flow isprovided, it is possible to avoid the multiplier altogether and to takethe through flow rate into account as a constant factor just as theother constants.

Thereafter the signal is supplied to a voltage frequency converter 36which produces a pulse frequency corresponding to the temperaturedifference and to the other influencing magnitudes, said pulse frequencyrepresenting unit quantities per unit of time. These pulses are suppliedto the input 37 of the OR-gate 32. If the two input signals of theOR-gate have a pulse duration which is very small relative to the pausesbetween the impulses, the the respective error which could occur due toa random coincidence between two pulses, may be disregarded. Where acomputer circuit is used, for example at 31 of FIG. 5 the calculation ofthe volumetric balancing correction factor may be completed to provide asignal output for control of the ultra-filtrate withdrawing pump 7. Inthis respect, the rate of ultra-filtration across the dialyzer membranemay be automatically controlled.

The arrangement shown in FIG. 5 represents but one example of a possibleembodiment. When the apparatus comprises a microcomputer, for example,for other purposes, it is suggested to use the micro-computer for thepresent purpose. Starting from the basic arrangement shown in FIG. 2,different embodiments of the dialysis solution circulatory system arepossible, whereby the difference may relate to the production of thethroughflow in the dialyzer as well as to the removal of air from thedialyzer circulatory system. Where circuit 31, for example, is amicro-computer, various control functions such as those mentioned above,may be included.

In an embodiment of the balancing chambers of the type shownschematically in FIG. 4 having a passively displaceable separationelement in the chamber, namely, the membranes 24 and 25, it is necessaryto provide an additional conveying device in series with the dialyzer inorder to produce the throughflow. A pump of any type is suitable forthis purpose. However, there is also the possibility to construct thebalancing chambers according to the principle illustrated in FIG. 6.

The balancing chamber 40 is separated into two chambers 40a and 40b bymeans of one movable or rather displaceable membrane 41. An energystoring device in the form of a coil spring 42 is arranged in one of thetwo chambers. The spring 42 rests against a support element 43 solidlyconnected to the membrane 41 in a sealing manner. In the position shownin FIG. 6, the two spaces in balancing chamber 40 are in equilibrium.The spring 42 is so dimensioned that it may displace the support element43 all the way to the outer wall of the space 40a and to retain aresidual force in this position.

In this manner the spring provides the driving force for the transportof the liquid out of the space 40a. The through flow speed depends onthe through flow resistance of the closed liquid circulatory system andmay be adjusted by means of a throttle to the desired value. The space40a comprises for its filling and emptying connecting ports 44a and 44b,whereas the space 40b is provided with connecting ports 45a and 45b.

The just described function of the balancing system assumes in any eventthat the medium present in the balancing chambers is practicallyincompressible. Thus, it must be prevented that air bubbles enter intothe balancing chambers. On the input side for the supply of freshdialysis solution this condition is assured without any difficultiesbecause it is necessary anyway to degas the dialysis solution before itreaches the dialyzer. For this purpose devices are known operating witha thermal or reduced pressure degassing and a subsequent removal of thegas bubbles.

According to the invention, a further air separator is necessary on thereturn flow side from the dialyzer to the balancing device in order toremove air which may enter the system, particularly due to leaks at thedialyzer connections or in other uncontrollable ways.

FIG. 7 shows a respective arrangement which comprises in addition to thefunctional elements described with reference to FIGS. 1 and 2, a pump46, an air separator container 47, and an air separator valve 48. Theair separator valve 48 is controlled by a level sensor 49. If the liquidlevel in the air separator container 47 sinks to such an extent that thelevel sensor responds, due to the air collected in the air separatorcontainer 47, the air separator valve 48 is opened in the conduit 3bwhich connects to the discharge conduit 3. In order to produce apositive pressure in the air discharge container 47 by utilizing thedrive force `d` of the pump 46, the return flow in the balancing deviceis additionally closed off in a suitable manner when the level sensor 48responds.

For example, this may be accomplished by closing the valves 19 and 20(FIG. 3) as schematically indicated in FIG. 7. The collected air isdischarged through the air discharge valve 48.

The level sensor 49 may for instance, be a reed contact which isactuated by a magnet provided with a float. The switching characteristicof the reed contact may be utilized advantageously for terminating theair removal when the liquid level in the removal chamber again exceeds apredetermined liquid level.

An example embodiment of a hemodialysis apparatus that has beenconstructed and which combines certain of the above described featuresas well as a few additional features will now be described withreference to FIG. 8, whereby the same components as in FIGS. 1 to 4 and7 are provided with the same reference numbers.

The liquid circulatory system schematically shown in FIG. 8 comprises asan essential component the balancing device already shown in FIG. 3including the two balancing chambers 22 and 23 and the respective valves14 to 21.

The supply of fresh dialysis solution to the balancing device takesplace under a certain pressure (about 0.3 to 1.5 bar) from the supplyunit 100 which, among others, also serves for degassing and heating thedialysis solution. The water entering through the water conduit 50 isreduced in its pressure by the pressure reduction valve 52 to a lowerpressure (0.1 to 1.0 bar).

The concentrate is admixed downstream of the pressure reduction valve.The concentrate is taken out of a concentrate container 53 through thedosing apparatus 9 and the conduit 51.

The dosing apparatus shown in FIG. 9 purely schematically has a housingA, B in which the membrane body C (for example, rubber) is located. Aplug end D is vulcanized into the membrane body and driven with adefined, if desired adjustable, stroke in the direction of the doublearrow G.

The non-return valves E, F are located on the other side of the membranehousing.

As explained with reference to FIG. 3 the operation of the dosingapparatus 9 is synchronized with the control of the balancing device sothat for each work stroke of the balancing device a corresponding workstroke or a defined number of work strokes of the dosing apparatus arecaused. The mixture is degassed by the reduced pressure (about -0.9 bar)produced by the pump 54 in combination with the flow resistance 55. Theflow resistance may either be constructed as a simple throttle or it maybe a control valve controlled by the reduced pressure.

The liberated air is separated through the air separator 56 and, forexample, conducted into the discharge conduit 57. The air separator 56may, as indicated, work with a float 56 controlled air outlet, or with alevel sensor which actuates a magnetic valve.

The degassed dialysis solution travels from the lower connection of theair separator 56 through the continuous flow heater 58 to the balancingdevice. The continuous flow heater comprises an electrical heater and atleast one temperature sensor 59. The continuous flow heater heats thedialysis solution to a temperature corresponding to about bodytemperature (38° C.). For this purpose the temperature sensor 59 and theheater 58 are operatively interconnected through a temperature control60 in a known manner.

The balancing device, as explained with reference to FIG. 3, is chargedin sequential work strokes with fresh dialysis solution of determinedquantities which are defined by the volume of the balancing chambers 22and 23. The dialysis solution travels during the pauses between thecharging work strokes through the overflow valve 61 again into thedegassing system. The dialysis solution flows during this time in aclosed loop circulatory system formed by the elements 54, 56, 58, 61,and 55. The mentioned high reduced pressure is always available at thesuction side of the pump 54. This high reduced pressure is used in theexample described here also for the purpose of removing the air from theair separator 47 located in the dialyzer circulatory system.

Referring to FIG. 8 the arrangement of the elements 54, 55, 56, 58, 61in a closed loop re-circulatory system is a special feature of thesupply unit 100 and so is the feeding of the dialysis solution into theconnecting conduit forming a junction between the flow resistance 55 andthe pressure maintaining valve 61. A high efficiency in the degassingand an advantageous control characteristic of the continuous flow heaterare achieved due to the re-circulation. Another advantage is seen inthat in this embodiment the dialysis solution is available underpressure which may be higher to any desirable extent than the waterinlet pressure at 50. Another advantage is seen in that simultaneously areduced pressure is available for sucking off of air out of othercomponents of the system. Although the closed loop arrangement of theelements 55, 54, 56, 61 is essential, the continuous flow heater 58could be arranged at another position of the circulatory system, forexample, directly ahead of the flow resistance 55 or between the flowresistance and the pump 54 or between the pump and the air separator 56.

The fresh dialysis solution coming from the balancing device travelsthrough the analyzing device 10 and the bypass valve 62 in the conduit63 leading to the dialyzer. The valve 62 is connected electrically by adashed line 83'to the analyzer 10 for controlling the operation of thevalve 62. The analyzing device 10 is, in the present instance, anelectrical conductivity meter combined with a temperature sensor whichserves on the one hand for the compensation of the temperaturedependency of the conductivity measurement and which, on the other hand,is used for measuring and monitoring the temperature of the dialysissolution as explained above with reference to FIG. 4. If theconductivity or the temperature is outside the permissible standardrange, the bypass valve 62 is automatically switched over so that thedialysis solution is not supplied anymore to the dialyzer, but rather itis detoured in accordance with the dashed arrow to the discharge side ofthe dialyzer.

During the normal function of the dialysis, solution coming from thedialyzer flows through the conduit 64, through the blood leakagedetector 65, and through the pressure measuring device 66 into the airseparator 47. The blood leakage detector and the pressure measuringdevice are known components for monitoring the leak tightness of thedialyzer membrane or for measuring the return flow pressure. The used-updialysis solution is returned from the lower portion of the airseparator 47 through the pump 67 to the balancing device. The conveyingcapacity of this pump, which may, for example, be varied by an r.p.m.adjustment of the drive motor 90 determines the quantity of dialysissolution flowing per time unit through the dialyzer.

The electrical signal 74 for the switch over of the valves of thebalancing device and for the synchroneous control of the dosingapparatus 9 is derived, in the actual embodiment of a hemodialysisapparatus, from the supply circuit 91 of the drive motor 90 of the pump67. If, namely, the membrane which forms a displaceable element in therespective balancing chamber serving for the supply of the dialyzer,reaches an end postion when it rests completely against the chamberwall, the power requirement and thus the current taken up by the pumpmotor 90 rise sharply. In this manner it is possible to derive theswitch over signal by means of a resistor 91' inserted into the motorcurrent circuit including the supply circuit 91 for the motor 90, saidresistor 91' being connected with the input of a threshold value switch74. The switch over signal 74 from the threshold value switch 74 isapplied to the input 74' of FIG. 3A when said motor current risessharply.

The air separator chamber 47 has in its upper portion a level sensor 49,for example, including a preheated thermistor operating in accordancewith another conventional functional principle. If the liquid level inthe air separating chamber 47 falls below the response level of thesensor 49, the valve 48 is opened by the switching signal of the sensor49 so that the air is sucked off through the conduit 68 through thedegassing pump 59 into the supply section 100. A reduced pressure of,for example, -0.9 bar is used for removing the air because in thedialyzer circulatory system also normally a reduced pressure prevailsranging up to about -0.6 bar depending on the adjusted ultra-filtrationrate.

The valve 48 is closed again when the liquid level in the air separatingchamber 47 has risen again sufficiently.

For the connection of a dialyzer which is not prefilled with the liquid,a special filling program is provided as has been explained above withreference to FIGS. 3 and 3A. The balancing function is suspended in thefilling program. However, the proportional dosing function of thebalancing device in combination with the dosing apparatus 9 ismaintained. The filling program is switched on automatically when theair removal operation through the valves 48 exceeds a predeterminedduration due to the large quantity of air coming from the dialyzer. Forexample, the filling program may be switched on by closing the switches75a and 75b in FIG. 3A through a timer which is connected with thesensor 49.

In this instance the valve 48 is closed and a valve 69 is opened inorder to conduct the air through this valve directly to the dischargeport 57. The valve control is modified in the manner described withreference to FIGS. 3 and 3A so that fresh dialysis solution is suppliedunbalanced to the dialyzer where it displaces the air present in thedialyzer into the air separator container 47. Thus, the air flowsthrough the opened valve 69 into the discharge port or conduit 57. Ifthe liquid level in the air separator container has risen again due tothe following dialysis solution, the filling program is terminated bythe respective signal of the level sensor 49 and the system is switchedover again to the normal balancing type of operation.

The removal of a precisely predetermined liquid quantity from thedialyzer circulatory system and thus the measuring and/or control of theultra-filtration takes place by means of the withdrawal device 7. Thewithdrawal device 7 is constructed, in the present example embodiment asa volumetric membrane pump, whereby each individual pump strokecorresponds to a quantity unit (1 milliliter) of ultra-filtrate. Thewithdrawal takes place through a conduit 83 from the lower portion ofthe air separator container 47 in order to make sure that only liquidfree of bubbles is being conveyed. The output of the ultra-filtrationpump or withdrawal device 7 is normally connected with the dischargeport or conduit 57 through the switch over valve 84. However, with theaid of the switch over valve 84 there is also the possibility toseparately discharge the withdrawn liquid in accordance with the dashedarrow through the sample conduit 85, and, for example, to gather thewithdrawn liquid in a measuring container 200 for control purposes.Thus, the rate of ultra-filtration may be regulated by a measurementsignal for controlling the pump 7 as heretofore described. For example,a signal representing the measured quantity of withdrawn or divertedultra-filtrate solution may be used to control the rate of thevolumetric pump 7 to maintain a specified rate of withdrawal or toachieve a desired quantity of withdrawn ultra-filtrate containingsolution. As one example the pump may be regulated for withdrawing afractional portion in the order of magnitude of 1/1000 of the totalultra-filtrate containing solution flow downstream from the dialyzer inthe dialysis solution circulatory system. Additionally, the withdrawingor diverting pump 7 may be regulated to maintain volumetric balance andequivalence between the upstream dialysis solution flowing into thedialyzer and the downstream ultra-filtrate containing solution flowingaway from or leaving the dialyzer despite temperature changes anddifferences, all as heretofore described.

Another characteristic feature resides in that the samples of the freshdialysis solution may also be taken through the connection of the inletto the bypass conduit 83 and through a suitable utilization of theswitch over valves 62 and 84, whereby the samples are taken through thesample conduit 85, for example, in order to control the composition ofthe dialysis solution by means of an external analyzing apparatus. Forthis purpose the valves 62 and 84 are brought into the positionsrepresented by the dashed arrows, by means of a selector switch, notshown, and the ultra-filtrate pump is switched to its maximal strokefrequency. The dialysis solution is then available in the sample conduit85.

Incidentally, a significant difference relative to prior artproportional dosing arrangements in hemodialysis devices resides in thatin the apparatus according to the invention the concentrate and thedialysis solution are dosed whereas in prior art devices the originalcomponents, namely, water and concentrate are dosed. Due to this featurethe apparatus according to the invention provides an essential advantagewith regard to the chemical disinfection of the apparatus. It isconventional and suitable to supply a concentrate of a disinfectantinstead of the concentrate used for the production of the dialysissolution, when the dialysis solution circulatory system is subjected toa chemical disinfection between treatments. Such disinfectantconcentrate provides the disinfection solution after dilution withwater. In prior art proportional dosing devices this means that allcomponents located between the water faucet of the apparatus and thedosing apparatus for the water as well as the dosing apparatus itselfare not included in the chemical disinfection because the addition ofthe concentrate takes place downstream of the dosing apparatus. Contrarythereto in the system used according to the invention the concentratedosing apparatus may, for example, be connected directly to the waterinlet of the apparatus so that the entire liquid conducting portion ofthe apparatus is included in the disinfection.

Incidentally, the main advantage of the supply unit 100 shown in FIG. 8is seen in that the degassing device or air separator 56 is located at apoint in the entire conduit system where the largest reduced or negativepressure prevails. Thus, gas that may be present in solution in theconduit system is subject to a suction effect causing the gas to bedrawn into the separator 56. Yet another important advantage of thisarrangement is seen in that the production of fresh dialysis solution iseasiest in this zone of reduced or negative pressure.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated that it is intended to coverall modifications and equivalents within the scope of the appendedclaims.

What is claimed is:
 1. In a hemodialysis apparatus, wherein freshdialysis solution is supplied to a dialyzer (4) by fresh dialysissolution supply means (50, 51, 52, 53) and spent dialysis solution isremoved from the dialyzer (4) by a withdrawal device (67), theimprovement comprising reduced pressure closed loop circuit balancingmeans (22, 23) for balancing a batch of fresh dialysis solution againstan equal batch of spent dialysis solution, valve and conduit meansoperatively connecting said supply means to said balancing means andsaid withdrawal device to said dialyzer and to said balancing means forsupplying batches of fresh dialysis solution through the balancing meansto the dialyzer while discharging corresponding batches of spentdialysis solution from the dialyzer through the balancing means, firstdegassing means (100) operatively interposed between said supply meansand said balancing means for degassing said fresh dialysis solution,second degassing means (47) operatively interposed between said dialyzerand said balancing means for degassing spent dialysis solution suppliedto said balancing means so that only batches of degassed fresh dialysissolution and of degassed spent dialysis solution are balanced relativeto each other, further conduit means (68) operatively interconnectingsaid first (100) and second (47) degassing means, and suction pump means(54) operatively connected in said further conduit means (68) forcausing a further reduced pressure in said further conduit means (68),said further reduced pressure being larger than said first mentionedreduced pressure for drawing air separated from said spent dialysissolution in said second degassing means (47) through said furtherconduit means (68).
 2. The apparatus of claim 1, wherein said firstdegassing means for the degassing of fresh dialysis solution comprise arecirculating path for a repeated degassing of fresh dialysis solution,said recirculating path comprising said pump means (54) having a suctioninlet and a pressure outlet, gas separator means (56) operativelyconnected with an inlet to the pressure outlet of said pump means (54),pressure maintaining valve means (61) connected to one side thereof to afresh dialysis solution outlet of said gas separator means (56), andflow impedance means (55) operatively connected in series between saidpressure maintaining valve means in a throughflow direction and to thesuction inlet of said pump means (54) for connecting the fresh dialysissolution outlet of said gas separator means (56) to the suction inlet ofsaid pump means (54), supply conduit means (50) for feeding not yetdegassed, fresh dialysis solution into the supply means, said supplyconduit means (50) being operatively connected to a junction betweensaid pressure maintaining valve means (61) and said flow impedance means(55), further supply conduit means operatively connected to saidpressure maintaining valve means (61), said flow impedance means (55)providing a flow impedance value such that at the suction inlet of saidpump means (54) a negative pressure is maintained, said pressuremaintaining valve means (61) providing in said further supply conduitmeans a positive pressure relative to atmospheric pressure, wherebyfresh dialysis solution is recirculated through said pressuremaintaining valve means (61) in a closed loop flow circuit during pausesbetween charging work strokes of said balancing means (22, 23) for aneffective degassing of fresh dialysis solution.
 3. The apparatus ofclaim 2, wherein said gas separator means (56) define a gas dischargeopening at a top portion thereof for discharging gas (at 57) out of saidgas separator means (56), and wherein said fresh dialysis solutionoutlet of said gas separator means (56) is located at a bottom portionof said gas generator means (56) for transporting fresh dialysissolution from said fresh dialysis solution outlet to said balancingmeans.
 4. The apparatus of claim 2, wherein said pressure maintainingvalve means (61) comprise non-return valve means providing a one-wayflow path toward the suction inlet of said pump means (54).
 5. Theapparatus of claim 2, wherein said gas separator means (56) compriselevel sensor means for controlling a gas outlet.
 6. The apparatus ofclaim 1, wherein said second degassing means (47) comprise controllablevalve means (48) in said further conduit means (68), and float valvecontrol means (49) in said second degassing means operatively connectedto said controllable valve means (48) for connecting said furtherconduit means and the reduced pressure in said further conduit means(68) to said second degassing means (47) in response to a filling levelin said second degassing means (47).
 7. The apparatus of claim 1,further comprising heater means (58) operatively interposed between saidfirst degassing means (100) and said balancing means for heatingdegassed fresh dialysis solution.
 8. In a hemodialysis apparatus whereinfresh dialysis solution is supplied to a dialyzer (4) by fresh dialysissolution supply means and spent dialysis solution is removed from thedialyzer by a withdrawal device, the improvement comprising closedcircuit balancing means (22, 23) for balancing a batch of fresh dialysissolution against an equal batch of spent dialysis solution; valve meansincluding valve control means and conduit means operatively connecting,said supply means to inlets of said balancing means, outlets of saidbalancing means to an inlet of said dialyzer, and said withdrawal deviceto an outlet of said dialyzer and to further inlets of said balancingmeans, for supplying batches of fresh dialysis solution through thebalancing means to the dialyzer while discharging corresponding batchesof spent dialysis solution from the dialyzer through the balancingmeans; and degassing means (47) operatively interposed between saiddialyzer and said balancing means for degassing spent dialysis solutionbefore a batch of spent dialysis solution is returned to said balancingmeans for balancing against a corresponding batch of fresh dialysissolution, said apparatus further comprising pump means (67) operativelyinterposed between said degassing means (47) and said balancing means, amotor means (90) for said pump means (67) and sensor means (91, 74) forsensing operation of said motor means, and wherein said balancing meanscomprise means defining two volumes and two flexible membranes, onemembrane in each volume, separating each respective volume into twochambers, said sensor means sensing an end position of said flexiblemembranes resting against a chamber wall by deriving a switch-oversignal from a supply circuit (91) connected to said motor means (90) forswitching over said valve control means when a sharp rise in motorcurrent occurs as a result of one of said flexible membranes reaching anend position.
 9. The apparatus of claim 8, further comprising levelsensor means (49) in said degassing means (47) for producing a controlsignal.
 10. A hemodialysis apparatus for withdrawing ultrafiltrate froma dialyzer, comprising balancing means including means defining twobalancing chambers (22, 23), a displaceable element (24, 25) in eachchamber dividing each respective chamber into two volumes thereby,defining four volumes (22a, 22b; 23a, 23b), namely one volume in eachchamber for fresh dialysis solution and one volume in each chamber forused dialysis solution, each volume having an inlet duct and an outletduct and a valve (14, 15, 16, 17, 18, 19, 20, 21) in each of said ducts,pump means (67) including pump motor means (90) for driving said pumpmeans, said pump means being operatively connected to those of saidducts cooperating with said volumes for used dialysis solution, freshdialysis solution supply means operatively connected to those of saidducts cooperating with said volumes for fresh dialysis solution, a pumpmotor current supply circuit including sensor means operativelyconnected to said pump motor means (90) for sensing pump motor currentin response to a respective displaceable element (24, 25) reaching anend position in a respective chamber whereby pump motor current rises,said sensor means including a threshold value switch means for producinga switch-over signal (74), said apparatus further comprising valvecontrol circuit means operatively connected to said valves forcontrolling operation of said valves, said valve control circuit meanshaving an input (74') operatively connected to receive said switch-oversignal (74) from said threshold value switch means for controllingoperation of said valves (14 to 21).
 11. The apparatus of claim 10,wherein said sensor means comprise a resistor in said motor currentsupply circuit.
 12. The apparatus of claim 10, wherein said pump meansare operatively connected to said inlet ducts of said volumes for useddialysis solution.